Set the modex as active before starting it. This resolves a hang in
MPI_Init() on comm-spawned processes.

cmr=v1.7.4:reviewer=rhc
btl/scif: do not return resource busy if we started a connection attempt.

Resolves a hang when using scif for shared memory transfers. This is a
simple change and doesn't require a review.

cmr=v1.7.4:reviewer=ompi-rm1.7